The most critical technology is the choice of eutectic material and the control of welding temperature. A new generation of InGaN high brightness LED, such as the use of eutectic welding, the bottom of the crystal can be pure tin (Sn) or gold tin (Au-Sn) alloy for the contact surface coating, grain can be welded to gold or silver coated substrate on. When the substrate is heated to a suitable eutectic temperature (Fig. 5), gold or silver elements penetrate into the gold-tin alloy layer, the change in the composition of the alloy layer increases the melting point, solidifies the eutectic layer, and heats the LED Sink or on the substrate (Figure 6). The eutectic temperature depends on the temperature requirements of the grain, substrate and device materials, and the temperature requirements for the subsequent SMT reflow process. Considering the eutectic solid crystal machine, in addition to high position accuracy, another important condition is a flexible and stable temperature control, plus nitrogen or mixed gas device, help in the eutectic process for oxidation protection. Of course, and silver paste solid crystal, to achieve high-precision solid crystal, depends on rigorous mechanical design and high-precision motor movement, in order to make the head movement and welding control just right, but also without damage to high yield and high yield The request.
The eutectic welding process can also be added to the flux, the biggest feature of this technology is no additional additional welding force, it will not be too large due to solid crystal welding and excessive eutectic alloy overflow, reduce the chance of LED short circuit.
Flip Chip welding
In recent years, it has been actively applied to high-power LED process. The method of rewinding is to join the GaN LED grain on the heat dissipation substrate. Because of the obstruction of the gold wire pad, it is helpful to improve the brightness. Since the current flow distance is shortened and the resistance is reduced, the heat generation is also relatively reduced. At the same time, such bonding can also effectively heat the heat transfer to the next layer of the substrate and then go outside the device. When this process is applied in the SMD LED, not only improve the light output, but also can reduce the overall product area, expand the application of the product market.
There are two main options for the development of the flip chip LED technology: one is Solder bump reflow technology and the other is Thermosonic welding technology. Lead solder ball welding (Figure 10) has been applied in the IC packaging for a long time, the technology is also mature, so no longer elaborate.
Thermosonic flip chip technology (Figure 11) is particularly suitable for high-power LED welding for low-cost and low-line device production. Gold to do the welding interface, because the gold itself, the melting point of the temperature than the lead silver ball and silver high, the crystal after the process design more flexible. In addition, there are lead-free process, the process is simple, reliable metal and other advantages. Thermal ultrasound finishing process after years of research and experience accumulation, has mastered the optimal process parameters, but also in several major LED manufacturers have been successfully put into mass production.
Foot production line, the rest of the large number (such as chip stickers, wire welding machine, testing machine, Tape machine) and other automation equipment are all dependent on imports.
Development of China 's LDD equipment industry specific proposals
Suggested that the state in support of LED technology and industrial development, the materials and process equipment as the basis for the development and the driving force to support. In the development of LED technology and industry in the process, I suggest that China take the "introduction, digestion, absorption, innovation, improve" the road. Specific programs are as follows: with the support of the state, through the country, LED manufacturing enterprises and equipment and materials manufacturing industry tripartite joint, the establishment of the incubator function of China LED equipment, materials, manufacturing and application of the Commonwealth.
(50% of the country, 15% of the equipment development unit, 15% of the chip manufacturing and packaging technology research unit, the LED chip), and the development of the high-end LED industry in China. In order to grasp and improve the equipment manufacturing level in a short time, Manufacturing and packaging enterprises 20%) to build a complete LED chip manufacturing and packaging demonstration production line. The demonstration line to solve the equipment development and process testing, LED product manufacturing process technology research and verification, to achieve complete sets of technology and process equipment supply has been. Where to participate in the demonstration of the construction unit, the right to free use of the production line for related products, technology and industrialization research and testing, in particular, LED product production units, priority concessions can be related research and industrialization results.
For the demonstration line, the implementation of three-step strategy, and ultimately to achieve the production of LED production equipment and localization (see the localization of equipment in Table 2). The first step: the use of two years or so, some of the key equipment for the localization (the state to give some bonus support); for the country has a certain basis and has the advantages of cost-effective equipment is the use of market competition principles, (For the development of standards); for some of the more difficult, short-term domestic equipment can not be made, the state should arrange research, and complete the production type ɑ prototype development. The second step, from the implementation of the third year of the program, the first step involved in the first two categories of equipment focused on solving the production process adaptability, production efficiency, reliability, appearance and cost issues, with domestic support and bulk Supply capacity, research equipment to complete the production model of commercial (γ - type) development. The third step, from the fifth year of implementation of the program, the first and second steps involved in all the equipment with international competitiveness, in addition to meet domestic demand, to occupy a certain international market; research equipment to meet the industrialization Production requirements and bulk supply capacity.